Project Summary A goal of many neurobiologists is to understand how the activity of cells and circuits in the brain relate to behavior, learning, and disease symptoms. In the past it was nearly impossible to establish the sufficiency and necessity of activity in specific cells to the generation or modification of a behavior. Optogenetics refers to a rapidly progressing set of tools that allow researchers to use light to read out and manipulate the activity of genetically defined brain cells. With optogenetics, it is now possible to use light to monitor the activity of cells during behavior and then add or subtract activity from these cells to establish the causal relationship between it and behavior. We request funds to help offset the costs of speakers and attendees to the 2020 Gordon Research Conference and Gordon Research Seminar on ?Optogenetic Approaches to Understanding Neural Circuits and Behavior?. This is the third such meeting, and the first two were fully subscribed, vibrant meetings that received excellent reviews. We have confirmed acceptances from nearly all the speakers to the 2020 meeting. We will use funds to partially pay for travel and registration fees (not food and drink) of speakers. We will prioritize the use of NIH funds to cover under-represented minorities, women, and junior scientists (non-tenured lab heads as well as postdocs and graduate students selected to give talks from poster presenters). The goal of the meeting is to gather a diverse set of scientists who can collectively present best methods for use of optogenetics, new tools, and recent discoveries made with optogenetics to an equally diverse group of young scientists interested in uncovering the relationship between circuit activity and behavior. 1